Subwoofer Tests: SVS, Paradigm, Velodyne and more. - Page 2

mike.e · 14th August 2005, 02:44 AM

What Im interested in is the velodyne servo feedback circuit,how it acheives such linearity compared to the other woofers. From what Ive seen it takes a good system to lower system harmonic distortion appreciably.

rcw · 14th August 2005, 03:12 AM

Philips had a similar system in the 70's, this used a velocity transducer mounted on the front of the voice coil I have forgotten the details of it.
At the time there was much discusion how you could do this by other means and the simplest way is to take a signal proportional to the back emf from the top of a resistor connected between the driver and ground, the second coil on a dual coil driver is also a possibility.

RobWells · 14th August 2005, 08:43 AM

A few years back I read an article about the phillips speaker. I think it was called a motional feedback speaker. (read it in HI-FI World I think)

I think the velodynes use an accelerometer in the dust cap as a sensor. I remember about 10 years ago velodyne released a 10" servo car sub driver that came with an electronic box of tricks that sat between the head unit and amp. The reviewers loved it, but I think it cost about £900 or £1200....

The servo subs do sound excellent. My friends got the Martin Logan Descent. 3x 10" drivers. In room sounds excellent. I was surprised by the amount of output from 'just' 3 10" ers.

Rob

mike.e · 17th August 2005, 07:17 AM

rcw: Ive read the EW article that used the 2nd VC as a pickup,it seemed to work in this case - the results werent too scientific.

Many seem to agree that making a good pickup + feedback circuit that doesnt oscillate is difficult.

rcw · 17th August 2005, 07:36 AM

Yes Mike, you have to be sure that the feedback is always negative other wise you end up with an oscillator.
Matlab has a control system toolbox that can model such things.

14th August 2005, 03:12 AM	#12
rcw diyAudio Member Join Date: Jul 2005 Location: sydney nsw	re servo Philips had a similar system in the 70's, this used a velocity transducer mounted on the front of the voice coil I have forgotten the details of it. At the time there was much discusion how you could do this by other means and the simplest way is to take a signal proportional to the back emf from the top of a resistor connected between the driver and ground, the second coil on a dual coil driver is also a possibility.

17th August 2005, 07:36 AM	#15
rcw diyAudio Member Join Date: Jul 2005 Location: sydney nsw	re feedback Yes Mike, you have to be sure that the feedback is always negative other wise you end up with an oscillator. Matlab has a control system toolbox that can model such things.

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14th August 2005, 02:44 AM	#11
mike.e diyAudio Member Join Date: Sep 2004 Location: NZ	What Im interested in is the velodyne servo feedback circuit,how it acheives such linearity compared to the other woofers. From what Ive seen it takes a good system to lower system harmonic distortion appreciably.

14th August 2005, 08:43 AM	#13
RobWells diyAudio Member Join Date: Aug 2002 Location: UK	A few years back I read an article about the phillips speaker. I think it was called a motional feedback speaker. (read it in HI-FI World I think) I think the velodynes use an accelerometer in the dust cap as a sensor. I remember about 10 years ago velodyne released a 10" servo car sub driver that came with an electronic box of tricks that sat between the head unit and amp. The reviewers loved it, but I think it cost about £900 or £1200.... The servo subs do sound excellent. My friends got the Martin Logan Descent. 3x 10" drivers. In room sounds excellent. I was surprised by the amount of output from 'just' 3 10" ers. Rob

17th August 2005, 07:17 AM	#14
mike.e diyAudio Member Join Date: Sep 2004 Location: NZ	rcw: Ive read the EW article that used the 2nd VC as a pickup,it seemed to work in this case - the results werent too scientific. Many seem to agree that making a good pickup + feedback circuit that doesnt oscillate is difficult.

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